okay let me try to help you.
Quite easy, use:
LicenseData "Your file with comments and "thanks".txt"
before you acctually begin with installing stuff. This means that you'll have to put license & thank's into one file though. But that won't be a problem I think.
You could try this at the end of the install section.
; prompt user, and if they select no, skip the following 3 instructions.
MessageBox MB_YESNO|MB_ICONQUESTION \
"The pack was installed. Would you like to run Winamp now with your AVS pack as the default plug-in?" \
WriteINIStr "$INSTDIR\Winamp.ini" "Winamp" "visplugin_name" "vis_avs.dll"
WriteINIStr "$INSTDIR\Winamp.ini" "AVS" "last_preset_name" "C:\PROGRAm FILES\WINAMP\PLUGINS\your path to your 1º preset\1º preset.avs
If this doesn't solve your problems just let me know and I'll help you again.